A quiet little spot where Rod Mollise shares his adventures and misadventures...

Sunday, August 28, 2016

Issue 507: Messier XI

M71: it's a glob!

We are now well past the halfway point and on the downhill
slope of the Messier list. Finally. I know it’s been slow going lately, but here’s another batch.
Unfortunately, these will have to last you for a while, since after a quick
breather I’m back on The Road again.
Anyhow, here’s seven more treats beginning with one of my absolute favorites.

M71

What does everybody want to know about Messier 71? Is it a globular star cluster or is it a
galactic (open) star cluster? What’s all the hubbub about, bub? One look will
show you. Get your scope on its position near the center of the little
constellation Sagitta’s arrow asterism, throw in a medium power wide-field
eyepiece, and you will soon be scratching your head. At first, it seems you
are looking at a rich galactic cluster. Like M11, maybe. But keep staring and
it becomes obvious it has a suspiciously strong central condensation.

So what’s the big problem? Let’s just take a look at M71's color
magnitude diagram. Unfortunately, that, too, is ambiguous. It could be an older galactic or it could be a younger globular. The
professionals wondered about this for many years, going back and forth on M71’s
classification. It seems pretty evident today, though, and has since the 1970s, that it is a glob, since the cluster’s HR diagram
does show a horizontal branch, which is a feature of globulars. The conclusion,
which has gained increasing credence over the last 40 years, is that it’s a
young glob of relatively high metallicity.

You don’t have to know pea-turkey about horizontal branches
and metallicity and color magnitude diagrams to appreciate M71, however; you
just have to like pretty things. M71 is a beaut when it’s riding high in its
little constellation, which lies just off the rich Cygnus Milky Way. I know it
looked good in my old (and sold) C8, Celeste, one long ago night, even from Chaos Manor South’s bright backyard:

This
curious cluster looks very much like an open cluster rather than a glob in the
light pollution. I can see quite a few cluster stars, but get only fleeting
glimpses of its core. The group seems shapeless. One of the big attractions of
this object, the beautiful rich field around it, is missing in the city. Still
a lovely sight, though. Best seen at 127x on this humid July evening.

M72

M72

Messier 72 is not a bad little cluster. If it were “only” an
NGC object it would actually be considered pretty good. But it is an M, and we tend to thing that should mean something special. This one is not special, but it is OK.

While it is fairly
loose with a Shapley – Sawyer concentration class of IX, and is dim for a
Messier glob at magnitude 9.2, M72's reasonably small size, 6.6’, means it stands
out well when it is well up and as far away from the horizon as it gets—which
is fairly high for most northern observers given the object’s -12 degrees
declination. The problem is locating the little booger if you don’t have goto
or digital setting circles.

Probably the best way to run down this Aquarius globular is
to move 3-degrees 22’ southeast of Abali, Epsilon Aquarii. This magnitude 3.75
star should be easy even in a smallish finder even in a suburban sky. When you
are on the spot (a magnitude 6.0 SAO star lies about 40.0’ to the northeast and
will be in the same field as the cluster in a wide-field ocular) scan around
carefully at medium power. Depending on your skies and scope, the globular may
be nothing more than a subdued round brightening of the sky background.

“Subdued round brightening?!” Yep, sorry; that’s about all
you will see from the typical backyard with a 4-inch or even 6-inch telescope.
An 8-inch will make it look “grainy” under those conditions, and may even
reveal a few stars around the periphery at high power, but to gain much
resolution, you’ll have to move that 8-incher to a dark site. How do you really
make the cluster look like much? Use a 10 – 16-inch under a dark sky. Still
ain’t gonna be M13, though.

M73

If you thought M72 wasn’t much, you really aren’t going to
be impressed by M73. What it is is a group of four stars that may not even be a
“real” deep sky object. This may just be an asterism, a pattern of stars
created by our line of sight. The collective brightness is not bad, 8.9. What
is bad is finding this little 3.0’ across patch of stars in the sun-poor wastes
of Aquarius.

The easy way to locate M73 is to go to M72 first. There,
move 1-degree 18.0’ almost due east. How hard is this thing to see? Even in a
4-inch, not that hard. What you have is a triangular pattern of four stars with
the brightest being just a bit dimmer than magnitude 10 and the dimmest being
almost at magnitude 12.

And that is kinda it. Use a medium-high power to get a nice
view of the group and move on. If it makes you feel better about spending your
time on this second-most-blah Messier of them all, perhaps this will make you feel
better: the group is now suspected to be
a (very old) open cluster and not just a “meaningless” asterism. Still feeling
put out about being here? The beautiful Saturn Nebula is 1-degree 45.0’ to
the northeast, so after you’ve seen all there is to see of puny M73, give
yourself a treat.

M74 “The Phantom”

M74

M74, the Phantom Galaxy, a beautiful near face-on Sc spiral
galaxy in Pisces, is one of the best Messier galaxies and also one of the true
wonders of the northern sky. Assuming you can see it at all.

At least getting on the proper position of this object is
not difficult without electronics. While Pisces is not the most striking
constellation in the sky, you should have no trouble spotting its magnitude 3.8
Eta star when the constellation is well away from the horizon. From there, move
1-degree 18.0’ northeast. Use a medium power ocular and search carefully for a
subtle glow in the field. And good luck.

M74’s size is a manageable 10’ 30”, and it’s “bright” for a
galaxy, magnitude 9.39. BUT. It’s a face-on and that almost always spells trouble. Its
light is badly spread out, making it quite difficult to see under less than
perfect skies. There’s a reason it is called the “Phantom,” alas. Many
observers consider it more difficult even than M101, and some folks claim it is
invisible from suburban skies.

Well, not quite. When I was writing my book, The Urban
Astronomer’s Guide, I hunted up M74 multiple times from a very compromised
site. It was often detectable in my 8-inch f/5 Newtonian at higher powers, and
was always visible with my C11. It wasn’t something that would put your eye
out, and there was no detail, but I could see it as a vague round brightening.

How do you get a good look at it, though? How do you see
spiral structure? It depends more on your conditions than your scope. The sky
needs to be dark, sure, but also dry.
Any humidity just kills this one. The seeing, the atmospheric steadiness, needs
to be good as well. When these prerequisites have been met, however, M74 has
shown off its spiral arms in stark relief to my rather humble 12-inch Dobsonian,
Old Betsy, as you can read here.

M75

This Sagittarius globular star cluster is a fairly bright
looking little guy despite shining at only magnitude 8.6. That’s because that
magnitude is coupled with a smallish size, 6.8’. While it’s somewhat low in
declination for some Northern Hemisphere observers, it’s not bad for most of us
at -21-degrees.

M75

Wanna look at it? Use a goto scope. You don’t own a goto?
Well, I’ll tell you how to find it, but you aren’t gonna like it. M75 lies in
the relatively unvisited part of Sagittarius to the northeast of the Teapot’s
“handle.” While it is technically in Sagittarius, it is right on the border of
Capricornus, and is easier to locate using the stars of the Seagoat.

The glob is 8-degrees southwest of one of dimmish Capricornus’
more prominent stars, Magnitude 3.0 Dabih, Beta Capricornii. 5-degrees 37’
farther to the northwest from the area of the cluster you’ll find a distinctive
pattern of 5th magnitude stars, a triangle of suns that’s easy in a
finder. While looking for M75, use a medium magnification eyepiece, and be on
the lookout for something that resembles a fuzzy star.

And a fuzzy star, or at least a bloated fuzzy star, is
about all you can expect in 8-inch and smaller scopes, even from fairly good
locations. To see a few stars you’ll usually need those good conditions and a
10-inch telescope and high power. 12-inches is decidedly better. In addition to
its small size, M75 has a couple of other strikes against it. It is a highly
compressed group—it is a Class I—and it is distant for a glob, lying some
67,500 light years from our cozy little rock.

M76 “The Little
Dumbell”

The skies have rolled on now, and the stars of winter are on
the rise, including the suns of Perseus. That constellation’s M76, a planetary
nebula, is one of the true beauties of the list. It’s a little small, about
3.0’ x 2.0’, but that makes it look bright even at its magnitude of 10.1.

Finding is not a hassle for the computer deprived. The
Little Dumbell lies about 7-degrees south-southwest of the magnificent Double
Cluster and 1-degree northwest of a magnitude 4.0 star, Phi Persei.

And when you get there? M76 is easy to see in small telescopes, being obvious with my 60mm ETX, Snoopy, from suburban light pollution. Doing more than just making out the nebula requires more aperture, however. In 6 – 8-inchers, the nebula looks like a, yes, small dumbbell (it looks
more like a dumbbell than its big brother M27) or maybe a peanut. With
10-inch and larger instruments you’ll begin to pick up dark patches and
streamers of gas. Whatever the size of your telescope, use higher powers on this small object and employ an OIII or UHC filter if you have one, as I did on one pleasant Chiefland Astronomy Village night
with my C11, Big Bertha:

M76
is very good this evening. In addition to the two lobes and brightness
variations across these lobes, the streamers of nebulosity wrapping around the
main body of the nebula are fairly easy to make out.

M77 “Cetus A”

M77 in 1990 with the Palomar Junior

What’s troubling you, Bunky? You are observing from your
light polluted backyard in the fall and want to see galaxies? M74 ain’t making
it with you? Well, there’s one island universe you can see under surprisingly
poor skies, M77, a face-on Sb spiral in Cetus. Now, I’ve already told you
face-ons are difficult. What makes M77 different? An intensely bright center.
This is an AGN (“active galactic nucleus”) object, a “Seyfert” galaxy, which
pumps its integrated magnitude up to 8.7. With a size of just 7’6”,
M77 is hard to miss even for small backyard scopes.

Finding is a trivial affair, since the galaxy lies less than
a degree southeast of a fairly prominent star (as the stars of Cetus go),
magnitude 4.0 Delta Ceti. Scan from Delta with a medium power wide field
eyepiece and you’ll soon run across a suspiciously fat star.

What’s the reward? You get to see a galaxy, if not one that shows
much in the way of details. As I discovered 26-years ago when I used my 4-inch
Palomar Junior to inspect M77 from my urban backyard:

Nice,
bright galaxy. Easily seen with direct vision but handicapped by its
southwestern position, which puts it right into the worst of the light
pollution. Round with a bright central region. Diffuse, round outer envelope.

And, frankly, that’s all you’ll see even with
considerably larger apertures from dark sites. 10-inch and bigger scopes will
make the galaxy’s actual (tiny, star-like) nucleus visible, however.

That is it, y’all. I’d like to keep going, but I’ve got to
turn to other tasks. I’ve got a Sky &
Telescope Test Report to get underway, and I need to at least think about
packing for my next gig, the Almost
Heaven Star Party. In my absence, why not get out and see some Ms for
yourself? Especially if you, unlike me, are lucky enough to live somewhere
where there’s a hint of fall in clear skies.